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I’ve finished my PhD. It was supervised by Julian Allwood:
This thesis reports on experiments into whether abrasives, lasers or solvents can remove ordinary black toner-print from ordinary white office paper in a way that leaves the paper reusable. If it could be ‘un-printed’ then waste office-paper could be reused immediately, without the need for recycling.
Paper and board consumption causes approximately 1% of man-made climate change gas emissions. Estimates in the ﬁrst chapter suggest that un-printing could reduce emissions per tonne of office paper by up to 95% – greater than the potential from incineration, localisation, annual ﬁbre, ﬁbre recycling, un-printing or electronic paper.
There has been no academic work on un-printing, but some relevant patents have been ﬁled. The second chapter reviews these patents according to whether they remove, obscure or de-colour the original print. It is not clear from the patents whether toner-print can be removed by abra- sives, lasers, or solvents without rendering the paper unusable. These three approaches are tested experimentally and the results reported in chapters 3, 4 & 5.
Abrasives can remove toner-print with limited damage to the underlying paper by operating in an adhesive wear regime. This involves making ten passes with a ﬁne P800 abrasive rubbing at high speeds (6 m/s) and low loads (0.3 N). Longer wavelength lasers are able to remove the toner-print and leave blank paper undamaged by operating at 1 W and 10 kHz in the 1064 nm wavelength and scanning across the surface eight times at 400 mm/s. Unfortunately the paper beneath the print is yellowed during removal. A 40:60 mixture chloroform and dimethylsulfoxide eﬀectively dissolves toner without dissolving paper if agitated with ultrasound for four minutes.
Chapter 6 outlines the research required to make the approaches feasible replacements for conventional paper recycling. The abrasive approach requires research into ex- tending abrasive life. The laser approach requires research into avoiding paper yellowing. The solvent approach requires research into benign solvents and solvent recycling. All three approaches would need to be tested on a wider range of prints and papers.You can download a pdf of this thesis. The work was continued by David R Leal-Ayala. In particular, ge got the laser based approach to work better.
Some of the material in my PhD thesis has been published in Journals and presented at conferences. In all cases my supervisor, Julian Allwood, was co-author: